How to get "unfiltered" array items?

Question

Let's say I have an array which I filter by calling myItems.filter(filterFunction1) and get some items from it.

Then I want to run another filtering function filterFunction2 against the remaining items which were not selected by filterFunction1.

Is that possible to get the remaining items that were left out after calling a filtering function?

Answer 1

You'd have to rerun the filter with an inverted predicate, which seems wasteful. You should reduce the items instead and bin them into one of two bins:

const result = arr.reduce((res, item) => {
    res[predicate(item) ? 'a' : 'b'].push(item);
    return res;
}, { a: [], b: [] });

predicate here is the callback you'd give to filter.